US2875143A

US2875143A - Push-pull power reactor

Info

Publication number: US2875143A
Application number: US598219A
Authority: US
Inventors: Darol K Froman
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-07-16
Filing date: 1956-07-16
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24
Also published as: GB855671A

Description

Feb. 24, 1959 D. K. FROMAN PUSH-PULL POWER REACTOR 5, Sheets-Sheet 1 Filed July 16, 1956 PIVITNESSESTI a *zvw Feb. 24,. 1959 D. K. FROMAN PUSH-PULL POWER REACTOR 5 Sheets-Sheet 2 Filed July 16, 1956 INVENTOR.

Daro/ K. Froman i i I i I i Fig 2 FebQ24, 1959 D.\K.' FROMAN $875,143

PUSH-PULL POWER REACTOR Filed Jul 'le, 195s s Sheets-Sheet s l l l I l I l l l l IOO O I l l l l l l l l l i 6375 6.875 7.375

Hsec) Fly 3 WITNESSES INVENTOR. W Daro/ K. Froman Feb. 24, 1959 D. K. FROMAN PUSH-PULL POWER REACTOR 5 Sheets-Sheet 4 Filed July 16, 1956 1 INVENTOR.

Daro/ K. Fro/nan WITNESSES'A' D. K. FROMAN PUSH-PULL POWER REACTOR Feb. 24, 1959 Filed July 16, 1956 w at WITNESSES] United. States Patent 2,875,143 PUSH-PULL rowan R -(tron Darol K. Frames, mementos, N. Mei, assigns; the

United States of America as represented by me United States Atomic Energy Commission 1 Application July 16, 1956, Serial No. 5985219 7 14 Claims. (e11. 204=1s4.2

i The preseht invention relates to-nuclar reactors and more particularly to homogeneous nuclear reactorsut'i plicated mechanical apparatus for circulating' the liquid fuel through heat exchanging apparatus; Further; these reactors generally utilize uranium-water solutions which involve the complex'problems associated .wtih radiqlytic dissociation :of thewater and the consequent problems of either recombiningthese radiolytic gases or of. safely venting them to the atmosphere. However, the useio f 2375,143 Fatentei'rl F e5. 24, 1959 the" liquid fuel. The increased vapor pressure will force the liquid fuel out oi the critical region through the heat exchanger and into the second critical region. As the liquid fuel in the sefcondbi'itieal region reaches a conditiofi of ciiticality the pres si'rr created in the vapor region of mes-edema reactor, thiough the evolution of energy in that reaction region, will force the liquid fuel back through the heat exchanging apparatus 'to' the first critical region. This metho'dof circulating the liquid :fuel provides a safe, simple and positive means for moving the liquid fuel through the heat exchanger, eliminates the necessityfor any moving parts in the reactor, and provides a self-regulatiiig sy st'eni.

M, M 05 is filled mi a liquid 9 q of nuclear emissar is reaenea arid the liqiiid fuel heats itself and expands to fill at least the 7 total volume at the critical regrets. The anneal ra lan homogeneous reactors for power producti on has well? knowna v t s. -r e e tly e ope atio be.- cause of; the negative temperature coeffieient, of tivi y n ompa a e e hrc in he flamma le material and products thereof from the tile}.

The present invention overcomes some 'of the prob lems pt the prior art reactors and ut'liz es a nevv and n el et o w wl i the li qis ue hrou h? heat exchanger. The preferred ernbod irnent gees riot re; quire,the gas handling and exhaust apparatus g any associatedrv ith reactors of the-prior an, andovei cofites 1 P r a i' iqv d tislri ql t e ar cated at opposite ends ther of and. contaihing heat as: changing apparatus. H i p A Although the description of the preferred embo 'm is specific "to an average power level of appro" 1y 1 megawatt at which the average thermal n fiux would be of the order of l.5 1 0 irutironsf cinF 'se'c. using ordinary water as a iiri'od 1am,- appro priate changes in the size, of the" critical reg ii; changing capacity and time irite'rval Between neutr n bursts may be made to provide a ower output of eithe'f larger or smaller value.

The preferred embodiment of the present invention provides for the circulation of the liquid fuelthrough the heat exchanger by means of the vapor pressure created in the vapor region abovethe critical region. 'lfhus when the liquid in the first critical region becomes critical; nu: clear power will be generated. The energy from the. nuclear reactions w;i lliheat the:1iquid fuel and. y se its above temperature, thereby increasing. the vapor pf'ssui'e difliculties and hazards ,gefiefally associated fie will have an excess k, but the excess will not be prohibitively' la'rge. This can be seen by considering that the critical region will never be filled with cold solution because the amount ofheat extracted from the liquid fuel up g through the heat exchanging apparatus is predetermined so that the liquid fuel moving into either critical geometry region; 'vvill'have a controlled temperature. The injection and/orexpansien of the liquid fuel in the critical geometry region will result in a gain in reactivity det'eriiiihed by the-geometry and temperature. The liquid fuel above the bottom of the bafile will have little etfect upon the reactivity 9f the critical region since, "f6? the tirn intefval dfifihg vvh iEh the liquid fuel exceeds thef haitleheight, the criticality ofthe system is ure. Thus the hegative temperature deficient of re ctivity will control the max ima enem in at b ret d i t l q i Thus, it is apparent that the reactor system of the present invention requires that a predetermined relatiofi eiists btivenfh temperature at Which the li'qii'id fiil first critical and the temperature at which the presvapor voliirh e is of siiliicirit value to force the l quid fuel fiito the second critical geometry region. Furthermore, the pressure in the vapor region above the first critical region must have a sufiiciently high value to in me that the second critical geometry regio'ii' ,Will be r r i hinimiim' entieal'v'aninr of liquid fuel, (pressure existing in the vapor region ture.

Therefore, it is" an object of the present invention to provide a homogeneous liquid fulnuclaf actor system in which a liquid tiil cifcula'ted thl ougha heat exchanger by means of the vapor pressure created above the critical region. I q

Another object of the pre'ser'it invention is to'provide such a fiuclear reactor s' fami' which neither requires mechanical means for circulating the fuel softener upon a temperature gradient to create convection currents.

A further object of present invention is to provide such a nucleaireactor system havihg are critical geometry regions connected through a heat exchanger.

Atstill'further ,object of the present invention is to provide such'a nuclear reactor system; which is so desig hed and constructed that: the temperature of the liquid fuel in. qr itipal regioncannotattain a value higher than a resl t m a d matr im- Other objects and advantages dith present invention will bcoiiie'appare'r'itfroni serous-wing description ing the. drair inghei'byi made a part of the specifica- Ei gii ire: 15 is pets I of the margins an: hodimentof he present invention; a a 1 Figure 2 is detailed sectional view of one of the reactors;

Figure 3 is a graph of one of the neutron bursts in terms of power and time;

Figure 4 is a graph of peak power with respect to time; I

Figure 5 is a graph of the liquid level of the liquid fuel in the two critical regions as a function of time;

H embodiment is a hollow container.

Figure 6 is a graph of the temperature of the liquid fuel in the two critical regions as a function of time; and I Figure 7 is a graph of the velocity of the liquid fuel into and out of the critical regions. Table I is a summary showing the order of magnitude of the various reactor specifications for the preferred embodiment.

TABLE I Power 1 megawatt. Fuel About 90%' enriched U03 iIl H3PO4.

Moderator Water.

Solution:

Composition -0-.6 M U0 in 5.6 1

Power density (average) -60 kw./liter.

Critical mass -2.5 kg. U

Total fissionable material -5.2 kg. U

Max. operating temperature 260 C. Max. oper. press. (excluding radiolytic gas and overpres- 1'' dia. thimble.

Overpressure 40 p. s. i. at 230 C.

and equal solution level in each reactor. Circulation of fuel:

Rate of cycle -1.5 sec. between consecutive bursts, -3 sec. between bursts within same critical region.

Temperature rise in each cycle 20-25". Min. temp. of fuel entering critical region 225 C. Temp. of fuel in critical region 240260 C.

Pressure in vapor space (excluding radiolytic gas and overpressure):

Before cycle -400 p. s. i. After cycle -600 p. s. i.

Apparatus The preferred embodiment of the present invention is shown in Fig. 1. It consists in general of two identical reactors identified generally as f20'and 21. Only one of the reactors will be specifically described; since each contains the identical components. The reactor 20 consists of a closed vessel 22 (see Fig. 2) which has a critical geometry region or vo1ume23 in its bottom "portion. The critical region 23 has a constant volume, i. e., liquid fuel above a baffle 24 is ineffective in adding, to thereactivity of the critical geometry. Above the critical 4 region 23 is located a baffle 24 which in the preferred The bafiie 24 is so centrally disposed as to create a cylindrical channel 25 which is non-critical by geometry.

It should be noted that in the preferred embodiment the baffle 24 is a hollow container which provides a channel 25 in which the liquid fuel would not be critical by geometry. However, it is within the purview of the present invention to provide bafiles of other design, such as a flat plate which may have neutron absorbers located above it. The plate and/ or poison will prevent the addition of reactivity to the critical region of the reactor. Located above bafile '24 is a vapor volume 26 which may be maintained non-critical by either geometry or the presence of neutron absorbing materials. Extending into the reactor through the vapor volume, the baflie 24, and into the critical region 23 is a safety rod thimble 30 which is sealed to the vessel 20 at the top and supports the baffle 24. Movably suspended within the safety rod thimble 30 is a safety rod 31 which is movable into and out of the critical region 23. I

Thevapor volume 26 contains a catalytic'recombiner 27 which consists of two vertically spaced plates 28 supported by the safety rod thimble 30. A catalyst 29 is supported between the plates 28 and is preferably in the 'formof pellets. The catalyst 29 recombines the radiolytically dissociated water moderator, i. e., the hydrogen and oxygen are recombined to form water vapor. The preferred catalyst 29 consists of platinized'alumina pellets in cylindrical form' with dimensions of 3 mm. by 3 mm. and having 0.3percent platinum by weight. The number of pellets required depends upon the amount of gas to be recombined. It is well known in the art that one such catalyst pellet will recombine 1 milliliter of hydrogen per minute with oxygen at 20 C. At higher temperatures the rate of recombination is increased. Thus at the operating temperature of the preferred embodiment the order of several thousand catalyst pellets would recombine the radiolytic gas. It should be noted that the'radiolytic gas, if not recombined upon initial contact with the catalyst, is passed over the catalyst several times by the expansion and compression of the gases in the vapor region.

It should be noted, however, that although the preferred embodiment specifies the use of a catalyst for recombination of radiolytic gas, it is within the purview of the present invention to use operating temperatures sufficiently high with the preferred liquid fuels so that recombination of the hydrogen and oxygen is automatic at the higher temperature and pressure. The only structural changes required would be to omit the catalyst and to provide a strong enough system to withstand the pressures. Such systems using automatic recombination are described in co-pending application S. N. 589,835, filed June 6, 1956, by Bidwell et al. entitled Nuclear Reactor Fuel Systems, the disclosure of which is incorporated herein by reference. I

The bottom of the critical region 23 is connected through a conduit 32 to a heat exchanger 33. The heat exchanger 33 has coolant inlet and outlet pipes 34. A transfer conduit 35 is connected to conduit 32, through a throttling valve 36 to a second heat exchanger 37. The throttling valve 36, however, is not necessary, as is explained hereinafter. The transfer conduit 35 is connected to conduit 38 which enters the bottom of reactor 21. The'components within the reactor 21 are the same as described for reactor 20. By-pass pipe 39 is-connected to conduit 32 through

valves

40 and 41 to conduit 33. The purpose of this by-pass connection isexplained in detail hereinafter. By-pass conduit-39 is also connected through safety line 42 to a rupture disk 43, through res-. ervoir line ,44 to a reservoir 45. The reservoir 45 is connected through a valve 46 to bypass conduit 39.

I The reactorvessel 20.has a pressurizi ng line '47- which connects the vapor volumedfithrough a valve 48 to a pressure supply line 49 and a ventline "The pressure supply line 49 is used to hiitially pressuriae the vapor volume with a selected gas, asexpla dininore detail hereinafter. The vent", use 50 'isfutrlizedi to "ventthe pressure within the vapor yolumelfi of either or both reactors 2 0 and 21 as may bereqiiired during jshutdown. Each reactor vessel 20 "and 21 'is surrounded by a stationary graphite reflector 51 which has a movablerefiector portion 52 adjacent to the

vessels

2,0 and 2 1. The movable portion 52 is used in temperature control and/ or compensating for fuel burnup. The "stationary graphite reflector 51 has an'induction. heater 53 arou'ndits periphery which is used during} start-up.

The

heat exchangers

33 and 37" liaveequal heat removing capacity and consist generally of a shell-, and tube-type heat exchanger where the tube or tubes are surrounded by the water which is flowing through inlet and outlet pipes 34.

It should be noted that heatexcha'rtger apparatus has approximately the same volume] as one of the. critical region-s so that practically all of the liquid fuel which is' passed through the heat exchanger during each cycle will be liquid fuelpwhichhas been heated in a critical region. Although these volumes do not necessarily need to'be equal, maximum heat transfer is attained when they are equal. u I

The heat exchanger design willldepend upon theapproximate power to be developed. by. the reactor., Further, such a heat exchanger must bje. capable of extracting only that portion of the available thermal energy which will not lOwer the liquid fuel temperature, upon ente iug a [critical region, below the minimumvalue, i. e., 225 Q, for extracting 1 megawatt of thermal energy in; the preferred embodimentf More .ther mal e iergyf may be extracted with due consideration for safetyg i. e., provided the solution temperature does not result in a prohibitively large excess k when injected. into a critical region. The minimum temperature, i. e., 225. in the preferred embodiment, maybe maintained, for example; by adjusting the flow rate and input temperature. of the coolant in pipes 34. However, it must. remove sufficient thermal energy, i. e., lower the: liquid fuel temperature so that the system will achieve a state. of stable operation. This latter temperature, for-the. preferred embodiment,- is approximately 240? C. f Liquid fuel The, preferred liquid fuel inthe reactorof the present invention is a solution of enriched uranium phosphate and phosphoric acid in Watenaltliough other liquid fuels may be used. The uranium is preferably enriched in the fissionable isotope U to a value of about 90%, however, other e'nrichmentsg as well as the enrichments .of-the' isotope U may be utilized in the liquid fuels. Specifically, the preferred liquid fuel has a compesition of approximately 0-.6 M U0 in 5.6 M- HPO The re actor using this liquid fuel isatlequately reflected so that prompt criticality is attainedfor the solution height approximately equal to the bathe height; i. e., the bottom of the baflie, and at a temperature of 250' C. The volume coefiicient of expansion of the fuei is such that.at 250 C. the liquid has expanded to" 1.1 8 times its room temperature value. Typical vapor pressure. values are 280 and'71 0 p. s. i.- at 225 arid Z7SfC. respectively.

aim-1 48 gas added to retard corrosion; Compression and expan- .sion of this gas during eaehhjalt cycle has an 'e'fiect on the operation of the reactor. In general, this gas overpressure is one of the determining factors in regard to the minimum power at which the system will operate.

Specifically, the higher the overpressure, the higher will be the minimum power level at whichthe system attains stable operation. Thus, in the system of the preferred embodiment the minimum power level for stable opera]- tion is of the order of three q'uarte'rs of one megawatt.

The temperature at which the liquid fuel euters the reactor is important for two reasons: (1).if the entry temperature is above a predetermined temperature the minimum power level will not be attained, i. e., stable operation is not possible; and (2) the entry of a large quantity of cold liquid fuel will result in prohibitively large excess reactivity. If the temperature of the liquid fuel entering a critical region is above a predetermined value, the system will'not achieve a state of stable e er' ating temperature. "For stable ope'ration the liquid fuel entering a reaction region of the preferred embodiment should have a temperature of not more than about 240C., where 240 C. results in approximately minimum power operation. For entry temperatures lower than this predetermined temperature, the temperature rises during a burst and therefore average power will increase. However, there is also a lower limit for the entry temperature, for the reason that the preferred system is designed to operate at an average temperature of 250 C. and the introduction of liquid fuel at a temperature of 100 for example, will result in very large peak powers and Very small e foldifng time s. Thus the minimum tempefa ture value is determined by' safety considerations, 'i. e., thee folding time required for safe operation.

Operation In starting up the reactor of the present invention, the] V into the sy'st'm,a t ambient temperature, issuflicient to The specific characteristics of the preferred liquid fuel and other liquid fuels which may be utilized are described in detail in above'r'eferenced co-pendin'g applications. N. 589.8 35. u j Since the reactor or the, present invention requires that a pressure be present in the vapor region 26f, the effect of different vapor region pressures can be seen by considering-that, in addition to the vapor above the liquid fuel solution there may be a non-eondensalile g'als in the region. This-may be uncut-named radfetytic j gas" or a fill one critical region to about the baffle height or slightly more and to fill the fluid. carrying means. including heat exchanging systeni located between the two aeaictors.

For the preferred liquid, the expansion of the liquid fueL'when the temperature is raised fromambient tem perature to operating temperature, will amount to about 18 percent. Thus, during operation there will bea small portion of the inactive critical region filled with liquid fuel. For stable operation a portion of the inactivecritical region should contain some liquid fuel.-

The equilibrium liquid level condition is changed iu the following manner. The inductance heating units 53 are activated to heat the liquid fuel in both critical re; gions. However, a temperature differential is maintained between the two. critical regions.- For the preferred embodiment, i. e., for a temperature swing of from 240 to 260, the initialcondition ofcriticality is attained when the critical region is just filledto the battle; however, such a condition in the liquid fuel ean be attained piily if the liquid fuel is at a temperature less than-about 25 C. Therefore, for this embodiment the liquid-fuel is initially heated to a temperature of less than ZSO byI the a liquid fuel level in reactor 21 which is at least about equal to the height of the baffle. The liquid fuel level in reactor 20 will be considerably lower. Criticality of the liquid fuel in the reactor 21 is not attained until after the safety rods 31 are removed. As the safety rods 31 are moved to their upper position in the vapor volume, as shown in Fig. 2, the liquid fuel in reactor 21becomes critical and the temperature is raised from the initial value of 240 C. to a value of about 260 C., during Which time the vapor pressure is increased so that a pressure differential is present between the vapor regions of reactor 20 and reactor 21, such a pressure differential being opposite to the initial pressure difference created by the 3 C. temperature differential. This pressure difference forces the liquid fuel out of reactor 21 into reactor 20. v

The condition of criticality attained during operation is one of prompt critical and a neutron burst of the general shape and characteristics shown in Fig. 3 takes place. The curve 60 of Fig. 3 .indicates that the maximum power developed, in terms of neutrons available, has a very sharp peak. As the power developed decreases, the effect of the delayed neutrons is apparent from the dotted portion 61 of the curve 60. At the point 62 of the curve 60, the effect of the liquid fuel level passing below the baffle 24 may be seen, i. e., the developed power decreases very rapidly after the liquid level passes this point.

Referring now to Fig. 4, it can be seen that the maximum power attained during the initial burst, as indicated by line 63, is considerably higher than the average power output of the preferred embodiment, where the average power is proportional to the area under the curve of Fig. 3. It should be noted, as can be seen by

lines

64, 65, 66 and 67, that the peak power is reduced after the first few initial bursts. .However, the average power, i. e., the area underthe curve of Fig. 3 is not reduced, since the effect of the delayed neutrons is to broaden the width of the curve shown in Fig. 3. The

lines

63, 65, and 67 represent the maximum power attained in reactor 21, while

lines

64 and 66 represent the maximum power attained in reactor 20. During the first few cycles of reactor operation, the period between power bursts is not necessarily constant. However, after the stable condition is reached for the preferred embodiment, the stable period between power bursts in any one of the reactors will be about 3.5 seconds.

Figures shows the relation between the heights of the liquid fuel in the reactor vessel and time. Curve 68 of Fig. is for reactor 21, which is the first to reach a condition'of criticality in the procedure outlined above. It should be noted that the maximum height of the liquid fuel reached in reactor 21 takes place shortly after the time at which the power burst takes place. This is also true during subsequent power bursts, as represented by lines 65 and 67. This is explained by' considering the fact that the liquid level may attain a height which is past the baffle 24, whereas the condition of prompt criticality is generally reached when this liquid level approaches the bottom of baffle 24. Thus, the liquid above the baffle has little effect on the reactivity in the critical region, since a condition of prompt criticality has been attained before the maximum height has been reached. Since the temperature of the liquid fuel has been significantly raised in a short interval. of time, the liquid will expand and the level of the liquid will exceed the battle height. -As the liquid fuel rises past the baffle the maximum temperature is controlled by the negative temperature coefficient of reactivity. Curve 69 of Fig. 5 is for reactor 20 and has the initial condition that only about 20 percent of the critical region is filled with liquidfuel. However, after' the initial burst 63,

the liquid fuel is-forced out of reactor 21, as is indicated by the downward sloping portion of curve 68, and into reactor 20, as is indicated by the upward slope of curve.

69. The fact that the second and subsequent maximums in the heightvof the liquid level are lower than the inital liquid levelhe'ight indicatesthat the initial starting conditions were more extreme than was required to attain a condition of stable operation. I

Figure 6 is a graph ofthetemperatureof the liquid fuelin terms of time. Curve 70 indicates the liquid temperature in reactor 21 while curve 71 indicates the liquid temperature reactor 20. It is apparent that reactor 21 has an initial starting temperature of 240, while reactor 21 has aninitial liquid fuel temperature of 243. 'At the time of the maximum power burst 63, the temperature of the liquid fuel in reactor 21 is raised to a value of about 260". After attaining a value of 260, the temperature declines slowly to a point 72 corresponding to the time when the liquid fuel is again reentering the reactor 21. At the point 72 cold liquid fuel starts to enter the reactor21 and the temperature drops more rapidly and a minimum temperature is reached at point 73. During this time the temperature of the liquid fuel in reactor 20 is being decreased by the entrance of cold liquid fuel, which is passed through the

heat exchangers

33 and 37. When the liquid height in the reactor 20 has reached its maximum value, as indicated by the first maximum of curve 69, a condition of criticality has already been reached in reactor 20, as is indicated by line 64. This condition results in at raising of the temperature of the liquid fuel in reactor 20 to a value of about 260. Thus, relative movement and temperature of the liquid fuel is opposite in'the two reactors providing a push-pull action. v

Figure 7 is a graph of the velocity of the liquid fuel in terms of time, where theplus values indicate the flow of the liquid fuelinto reactor 20. The curve 74 has an initial value of zero since, under the original starting conditions, the liquid fuel was not flowing. After the control rods are removed, the power burst .63 takes place and the temperaturerises from 240 to'260 C. As aresult the vapor pressure created in the vapor region 30 of reactor 21 forces the liquid fuel but at a velocity which increases rapidly until approximately the same time the'maximum temperature is reached, as indicated in Fig. 6. The velocity then decreases slowly until the power burst 64 in" reactor20 takes place. At the time that the temperature in reactor 20 is increasing, i. e., at

the time of power burst 64, the velocity into reactor 20 decreases to zero and reverses. The time at which the velocity is at zero corresponds to the time when the height of'the liquid fuel in reactor 20 is at maximum. Thus, it is apparent from Figs. 3 through 7 that the liquid fuel will 'be'moved from one critical region to another with a condition of prompt criticality being attained in each critical region. These figures also indicate that, after the first few cycles, a stable state of operation is attained. The data which is represented by these figures is for the particular case of a reactor operating between 240 and 260 C. It is within the purview of the present invention to operate in either higher or lower temperature ranges depending upon what the initial condition of criticality is. As stated above, for the preferred embodiment, the initial condition of criticality is attained when the preferred liquid fuel just fills the critical region and is at a temperature not exceeding 250 C.

. As is pointed out in the above-referenced co-pending application S. N. 589,835, the preferred liquid fuels require an initial overpressure of gas, i. e., oxygen or hydrogen, to maintain the liquid fuel thermally stable and to aid in corrosion protection. Such an overpressure of gas may beprovided through pressure supply line 49,

valve 48, and pressurizing line 47. The pressure supply line is connected to a source ofthe gas to be utilized. The overpressure is preferably provided during the time that the liquid level of each reactor is the same.

The time between consecutive power bursts and tem Fig. 1 by by-pass pipe 39. .The

valves

40 and 41 in lay-pass conduit 39 may be operated remotely to control the amount of throttling which is accomplished by the orificein throttle valve 36. i

In comparing the temperature swing during the operation of one of the reactors fora system which is throttled, to one which is unthrottled, it has been found that the throttled system resultsin an average power output which is between and 30 percent of the unthrottled system value. These values are based upon the assumption that the average power, to a-first approximation, is directly proportional to the period. f

Should the pressure in the system exceed a predetermined maximum, for example, 2000 p. s. i., the rupture discs 43 would operate-to remove the liquid fuel through reservoir line 44 to a non-critical reservoir 45. The valve 46 remains in a closed position during normal operation. Shut-down=is accomplished by insertingthe control rods 31 into the critical regions.

Although the preferred embodiment utilizes liquid fuels consisting of uranium phosphate, phos'phoric'acid and water, it is within the purview of'this invention to use conventional homogeneous reactor liquid fuels, such as uranyl sulfate and uranyl nitrate. Such liquid fuels would require low operating temperatures because of their thermal instability at higher'temperatures.

While presently preferred embodiments of the invention have been described, it is clear that many other modifications may be made Without departing from the scope of the invention. For example, such modifications may include the use of cycling control rods, i. e., rods which are automatically moved into and out of the critical regions with a predetermined but variable oscillatory period, to change the power burst cycle period, or the use of an initial pressure differential during startup which is a result of supplying different initial overpressures of gas. Therefore, the present invention is not appended claims. a

limited by the foregoing description but solely by the What is claimed is:

l. A homogeneous nuclear reactor system comprising in combination a first closed vessel defining a first constant volume critical volume, a second closed vessel defining a second constant volume critical volume, fluid carrying means connecting the bottom of said first critical volume to the bottom of said second critical volume, heat exchanger means located in said fluid carrying means, a quantity of liquid fissionable nuclear fuel in said system sufiicient at ambient temperature to approximately fill one of said critical volumes and said fluid carrying means, and means for moving said fuel through said fluid carrying means to alternately depress the level of said fuel in one said critical volume at least below the level required for neutronic criticality and raise the level in said other critical volume to the level required for prompt neutronic criticality.

2. A homogeneous nuclear reactor system comprising a first vessel defining a first constant volume critical volume, a second vessel defining a second constant volume critical volume, each vessel also defining a vapor volume above each of said constant volume critical volumes, fluid carrying means connecting the bottom of said first critical volume to the bottom of said second critical volume, heat exchanger means located in said fluid carrying means, a quantity of liquid fissionable fuel in said system sufficient at ambient temperature to approximately said first critical volumebeing sufiicient' toQdepress the remaining fuel below neutronic criticality and said quantity of liquid fuel transferred to said second reactor when added to any said liquid fuel thereinbefore present being sufficient to attain prompt neutronic criticality therein.

3'. The nuclearreactor of claim 2' wherein said fluid carrying means has a'vo'lume approximately equal to one of said critical volumes of said vessels.

4. A homogeneous nuclearreactor comprising a, first vessel containing a constant volume critical volume, a non-critical vapor volume above said critical volume, a bafile located between said critical volume and said va; por volume, said baffle defining the upper extremity, of said critical volume, a second vessel containing a constant volume critical volume, a second non-critical vapor volume above said second critical volume, a second battle between said second critical volume and said second vapor volume, said second baflle defining the upper extremity of said second critical volume, fluid carry.- ing means connecting the bottom of said first critical vol ume of said first vessel to thebottom" of said second critical volume of said second vessel, heat exchanger means located in said fluid carrying means, a quantity of liquid fissionable nuclear fuel in said system sufficient at ambient temperature to approximately fill one of said critical volumes of said vessels and said fluid carrying means, and means including said first and second vapor volumes and said first and second bafiles for alternately filling said first and second constant volume critical volumes to a level at least as high as said baffles so that a condition of prompt nuclear criticality is alternately attained in said first and second critical volumes and said liquid fuel is transferred from one of said constant volume critical volumes to the other of said constant volume critical volumes by means of the pressure in said vapor volumes.

5. The homogeneous nuclear reactor of claim'4 wherein said fluid carrying means includes means for variably throttling the liquid flow between said first and second constant volume critical volumes.

6. The homogeneous nuclear reactor of claim 4 wherein said fluid carrying means includes means for throttling the flow of liquid fuel between said first and second constant volume critical volume, and wherein variable fiow duct means is provided by-passing said throttling valve.

7. The homogeneous nuclear reactor of claim 4 wherein said first and second constant volume critical volumes are enclosed by neutron reflecting means, and wherein means external to said constant volume critical volumes are provided for selectively heating the liquid fuel within said first and second constant volume critical volumes.

8. The homogeneous nuclear reactor of claim 4 wherein said fluid carrying means has a volume approximately equal to the volume of one of said constant volume critical volumes.

9. A homogeneous nuclear reactor system comprising a first reactor vessel and a second reactor vessel, said first and second reactor vessels each containing a critical volume, a non-critical vapor volume, and a baffie separating said critical volume from said non-critical vapor volume, fluid carrying means connecting the bottom of the said critical volume of said first reactor vessel with the bottom of said critical volume of said second reactor vessel, a quantity of liquid fissionable nu clear fuel in said system, said quantity being sufficient .at ambientteinperature to fill one critical volume and said fluidcarrying means, said fluid carrying means including means for extracting heat from said liquid fuel, means for selectively heating the liquid fuel in said critical volumes whereby an initial temperature differential may be created between the subcritical quantities of liquid fuel in said first and second reactor vessels, said temperature differential resulting in a pressure differential between said vapor volumes thereby raising the liquid level in one of said critical volumes to at least said bafile, means for attaining a condition of prompt criticality in said one critical volume, thereby creating a" pressure in said vapor volume which forces the liquid fuel from said one critical volume through said fluid carrying means and said heat extraction means to the other of said critical volumes.

10. The homogeneous nuclear reactor system of claim 9 wherein said bafile consists of a hollow, closed container centrally disposed in said first and second reactor vessels, said container forming a cylindrical, non-critical channel, said channel connecting said critical volumes with said vapor volumes.

11. The homogeneous nuclear reactor system of claim 9, wherein said fluid carrying means includes means for variably throttling the flow of liquid fuel between said critical volumes.

12. The homogeneous nuclear reactor system of claim 9 wherein said fiuid carrying means has a volume approximately equal to one of said critical volumes.

13. A homogeneous nuclear reactor comprising a first vessel defining a first constant volume critical volume, a second vessel defining a second constant volume critical volume, fluid carrying means connecting the bottom of said firstcritical volume with the bottom of said second critical volume/heafe'xchanger means located in said fluid carrying means, a quantity of aqueous liquid fissionable nuclear fuel in said system sufiicient at ambient temperature to fill one of said critical volumes and said fluid carrying means, each said vessel also defining a vapor confining volume above each of said critical volumes for confining vapor and gases evolved from said heated liquid fuel, whereby said confined vapor and gases will force said liquid fuel out of one of said critical volumes into the other'of said critical volumes when a predetermined pressure exists in said vapor confining means.

14. The reactor of claim 13 wherein said vapor vol.- umes defined by said vessels contain means for recombining radiolytically dissociated hydrogen and oxygen.

References Cited in the file of this patent Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, vol. 3, held in Geneva 8-20, 1955. Library date Dec. 27, 1955 pp. 283-286, 265-272..

LA-1942, U. S. Atomic Energy Commission by L. D. P. King, Apr. 13, 1955 pp. 4-15 (available from ABC Technical Information Service, Oak Ridge, Tenn.)

NAA-SR-1525, Program Review of the Water Boiler Reactor Kinetic Experiments, by Atomics International, issue date Mar. 15, 1956, pp. 23-32.

Claims

1. A HOMOGENEOUS NUCLEAR REACTOR SYSTEM COMPRISING IN COMBINATION A FIRST CLOSED VESSEL DEFINING A FIRST CONSTANT VOLUME CRITICAL VOLUME CRITICAL VOLUME, FLUID FINING A SECOND CONSTANT VOLUME CRITICAL VOLUME, DECARRYING MEANS CONNECTING THE BOTTOM OF SAID FIRST CRITICAL VOLUME TO THE BOTTOM OF SAID SECOND CRITICAL VOLUME, HEAT EXCHANGER MEANS LOCATED IN SAID FLUID CARRYING MEANS, A QUANTITY OF LIQUID FISSIONABLE NUCLEAR FUEL IN SAID SYSTEM SUFFICEINT AT AMBIENT TEMPERATURE TO APPROXIMATELY FILL ONE OF SAID CRITICAL VOLUMES AND SAID FLUID CASRRYING MEANS, AND MEANS FOR MOVING SAID FUEL THROUGH SAID FLUID CARRYING MEANS TO ALTERNATELY DEPRESS THE LEVEL REQUIRED ONE SAID CRITICAL VOLUME AT LEAST BWLOW THE LEVEL REQUIRED FOR NEUTRONIC CRITICALITY AND RAISE THE LEVEL IN SAID OTHER CRITICAL VOLUME TO THE LEVEL REQUIRED FOR PROMPT NEUTRONIC CRIATICALITY.